The Effect of Ultrasonic Excitation on Ice as a Substitute for Natural Gas Hydrates

Philipp Zellnig

Research output: ThesisMaster's Thesis

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Abstract

In recent years, field tests and laboratory investigations have demonstrated that applications of ultrasound in the oil industry are versatile and in many cases not only technologically feasible, but also serve as an economical, sustainable and efficient alternative to currently accepted methods. This thesis focuses on the understanding of ultrasonic treatment in different disciplines throughout the oil industry and especially gives insights of the behavior of ultrasonic waves on ice as a substitute for natural gas hydrates and further aims at their safe, efficient and environmentally friendly removal. The formation of hydrates is one of the problems occurring during production, processing and transportation of natural gas. Incidents directly or indirectly associated with hydrates and their mishandling cost the natural gas industry millions of dollars. Even worse is the threatening of human lives due to accidents or improper operations. Therefore, the inhibition of hydrate formation and the effective removal of hydrate precipitations and plugs are a crucial task to understand and prompt constant improvement. Three different sets of experiments are performed to evaluate the effect of ultrasound on ice. For first orientation (Setup 1), a simple household ultrasonic cleaner with a basic setup is used. An instant effect is visually and acoustically perceptible after the ultrasonic signal is turned on. Small air bubbles emerge at certain spots inside the block of ice as a result of ultrasonic cavitation. Fractures and cavities are further results of the mechanical energy input. In the best case, the disintegration of the ice block was 24 times faster than under ambient conditions. Setup 2 compares the duration of ice plug removal in a prototype steel cylinder. A much faster disintegration of the ice plug is reached under ultrasonic excitation. Further, the mechanical properties of ice drastically change under ultrasound as the plug gets very brittle, instable and breaks easily. The main focus lies on Setup 3, as the steel cylinder is pressurized to get information about the temporal dissolution of the plug under pressure and the influence of changing ultrasonic fields. Pressure breakthrough times are evaluated in this set of experiments. The breakthrough time is a crucial parameter as it clarifies at which point a pressure or flow communication between an inlet and an outlet is granted. Therefore, it represents the time how long it takes until a plugged pipe can flow again. Further, different ultrasonic energy inputs are compared. Throughout all experiments under ultrasonic excitation faster disintegration of ice and decreasing breakthrough times are observed. In most cases an increase in energy does not necessarily mean a higher efficiency of disintegration, which approximately remains constant as long as any ultrasonic signal is applied. All experiments in this thesis investigate the effect of ultrasound compared to a non- sonicated system at ambient conditions. Further comparison to other common removal methods require additional experiments.
Translated title of the contributionDie Wirkung von Ultraschallwellen auf Eis als Ersatz für Gashydrate
Original languageEnglish
QualificationDipl.-Ing.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Pavlov, Mikhail, Supervisor (internal)
  • Hofstätter, Herbert, Co-Supervisor (internal)
Award date19 Oct 2018
Publication statusPublished - 2018

Bibliographical note

no embargo

Keywords

  • ultrasound
  • ultrasonic excitation
  • gas hydrates
  • hydrate remediation

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